The religion will pull it's followers towards the era attached to it. If the era is in the future from the current era, then those followers will seem to be forward-thinking folk. They will be innovators. If the era is in the past from the current era, then it's followers will seem more stable. They will be traditionalists. Each has its strong points, and each has its weaknesses.
This is not to say that it is possible that two people can have the same religion. There are allways changes that a religion will undergo when it is accepted into a person's worldview. The religion becomes changed by the accepting process. The worldview becomes altered by the accepted religion. Each person has their own unique religion, yet it is possible for many people to share the same base religion which led to the one they have accepted. Thus they all can identify as being of the "same" religion and they call themselves by that label.
The era associated with a given base religion is rarely changed when it is accepted into a person's mind. Sometimes a person's worldview is strong enough that the era they have chosen for themself remains intact and they alter the religion's attached era to be replaced by their own (or, at least, a slightly modified version thereof). Yet these are rare cases and they often have to alter the base religion significantly enough that they are not considered to be very devout by other members of the given religion.
Two religions that have the same era attached will exhibit similar characteristics. The era gets attached to a religion thru that religion's ideals and core values (which is why it is almost never altered when accepted into a worldview). Thus it follows that if two religions have the same era attached, they will likely share a lot of the same values and will only differ in some minor details. The basic ideas will be the same, it's the implimentation of those ideas that will differ.
The most clashing will occur between religions with the same era attached. When a religion meets another religion with an entirely different era attached, they will call each-other heathens (of course), but there will not be very much for them to argue over, as they can barely understand one another. When two religions attached to the same era meet, they can understand each-other very well, and will bicker to no end over the minor details upon which they disagree.